The previous article introduced the mechanism of action of cellulose ethers. And the next article will introduce some basic cellulose ether classifications.
1.1.1 Methyl cellulose (MC) molecular formula \[C6H7O2(OH)3-h(OCH3)n\]x
Refined cotton is treated with alkali and made into cellulose ether after a series of reactions with methane chloride as the etherizing agent. The general degree of substitution is 1.6~2.0, and the solubility varies with the degree of substitution. It is a non-ionic cellulose ether.
(1) Methyl cellulose is soluble in cold water, hot water dissolution will encounter difficulties. And its aqueous solution is very stable in the range of pH=3~12. It is compatible with starch, guar gum, etc. and many surfactants. When the temperature reaches the gelation temperature, gelation phenomenon will occur.
(2) The water retention of methyl cellulose depends on its addition amount, viscosity, particle fineness and dissolution speed. Generally, the water retention rate is high when the addition amount is large. The fineness is small and the viscosity is large. The amount of addition has the greatest effect on the water retention rate. And the viscosity is not directly proportional to the water retention rate. The dissolution rate mainly depends on the degree of cellulose particle surface modification and particle fineness. Among the above several cellulose ethers, methyl cellulose and hydroxypropyl methyl cellulose have higher water retention rate.
(3) The change of temperature can seriously affect the water retention rate of methyl cellulose. Generally the higher the temperature, the worse the water retention. If the mortar temperature exceeds 40℃. The water retention of methyl cellulose will become significantly worse, which will seriously affect the constructability of mortar.
(4) Methyl cellulose has obvious influence on the constructability and adhesion of mortar. The “adhesion” here refers to the adhesion force felt between the worker’s applicator and the wall substrate, i.e. the shear resistance of the mortar. If the adhesion is large, the shear resistance of the mortar is large, and the force required by the workers in the process of use is also large, and the workability of the mortar is poor. In the cellulose ether products methyl cellulose adhesion is at a medium level.
1.1.2 Hydroxypropyl methyl cellulose (HPMC)
Molecular formula is \[C6H7O2(OH)3-m-n(OCH3)m,OCH2CH(OH)CH3\]n\]x Hydroxypropyl methyl cellulose is a cellulose species whose production and dosage are rapidly increasing in recent years. It is a non-ionic cellulose mixed ether made by a series of reactions with propylene oxide and chloromethane as etherizing agents after alkalinization treatment of refined cotton. The degree of substitution is generally 1.2~2.0. Its properties vary by the ratio of methoxy content and hydroxypropyl content.
(1) Hydroxypropyl methyl cellulose is easily soluble in cold water and will encounter difficulties in hot water dissolution. However, its gelation temperature in hot water is significantly higher than that of methyl cellulose. The dissolution in cold water is also greatly improved compared with methyl cellulose.
(2) The viscosity of hydroxypropyl methyl cellulose is related to its molecular weight. And the viscosity is high if the molecular weight is large. Temperature also affects its viscosity, the temperature increases, the viscosity decreases. But its viscosity high temperature effect is lower than that of methyl cellulose. Its solution is stable when stored at room temperature.
(3) The water retention of hydroxypropyl methyl cellulose depends on the amount added, viscosity, etc. Its water retention rate under the same amount of addition is higher than that of methyl cellulose.
(4) Hydroxypropyl methyl cellulose is stable to acid and alkali. And its aqueous solution is very stable in the range of pH=2~12. Caustic soda and lime water, there is no significant impact on its performance. However, alkali can accelerate its dissolution rate and improve the viscosity pin. Hydroxypropyl methyl cellulose has stability to the general salts. But when the salt solution concentration is high, hydroxypropyl methyl cellulose solution viscosity has a tendency to increase.
(5) Hydroxypropyl methyl cellulose can be mixed with water-soluble polymer compounds and become a uniform, higher viscosity solution. Such as polyvinyl alcohol, starch ether, vegetable gum, etc.
(6) Hydroxypropyl methyl cellulose has better enzyme resistance than methyl cellulose. And the possibility of enzymatic degradation of its solution is lower than that of methyl cellulose.
(7) The adhesion of hydroxypropyl methyl cellulose to mortar construction is higher than that of methyl cellulose.
Landcel’s HPMC can be well used in wall putty, construction type mortar such as plaster mortar, self-leveling mortar, joint filling mortar, dry mix mortar, masonry mortar. We can customize according to customers’ needs and mail samples.